Controlling device for cooking apparatus



July 25, 1950 M. J. BOCK CONTROLLING DEVICE FOR COOKING APPARATUS 3 Sheets-Sheet 1 Filed Dec. 14, 1946 July 25, 1950 M. J. BOCK conmomfiuc DEVICE FOR COOKING .QPPARA'I'US Filed Dec. '14; 1946 3 Sheets-Sheet 2 Mt/EA/TOA may/y J. aoc/r y 1950 M. J. BOCK 2,516,503

poNT o 'INc DEVICE FOR COOKING APPARATUS Filed Dec. 14, 1946 3 She ets-Sheet 5 l/l/ I J F/GO'.

/A/l//VTOR MIMI/IA a. soc/r Patented July 25, 1950 UNITED STATES PATENT OFFICE CONTROLLING DEVICE FOR COOKING APPARATUS Application December 14, 1946, Serial No. 716,353

6 Claims.

.This invention relates to. a controlling device, and more particularly to a weight-responsive switch for a radio-frequenc cooking device.

In a certain type of microwave cooking apparatus, radio-frequency energy, for example in the microwave region of the frequency spectrum, is supplied from a high-frequency source, such as a discharge device of the so-called magnetron type, to a hollow wave guide or horn, along which such energy is propagated to impinge on food placed adjacent the open end thereof, thereby heating the same.

Energy is absorbed by the food when such is present at the mouth of the horn, so that the amplitude level of energy reflected from a refleeting surface (which is placed on the opposite side of the food from the horn) is quite low when food is present. Since the reflected energy level is low, the standing wave ratio in the horn and in the magnetron output line is also low. This is the desired or optimum condition of op-- eration, since magnetrons operate most efficiently when the standing wave ratio in the radio-frequency system is low.

When food is not present at the mouth of the horn, there is nothing to absorb the microwave ene gy, so that a large proportion of the energy is reflected from the reflecting surface, producing a high standing wave ratio in the radio-frequency system, such a ratio being detrimental to the operation of the magnetron and being, therefore, undesirable.

An object of this invention is to devise a means, responsive to the absence of food in the food tray of a microwave cooker, for cutting off the radiofrequency energy supply from the horn of said cooker.

Another object is to provide a means for preventing the setting up of a high standing wave ratio in a radio-frequency transmission system.

A further object is to devise a weight-responsive protective means for a microwave cooker.

A still further object is to devise a weightresponsive switch for connecting a magnetron to a supply voltage source.

The foregoing and other objects of the invention will be best understood from the following description of some exempliflcations thereof, reference being had to the accompanying drawings, wherein:

Fig. 1 is a longitudinal vertical sectional view through a portion of a microwave cooker utilizing one embodiment of the invention;

Fig. 2 is a vertical sectional view taken at right angles to Fig. 1;

Fig. 3 is a view similar to Fig. l but of another embodiment;

Fig. 4 is a horizontal sectional view of the device of Fig. 3;

Fig. 5 is a view similar to Fig. 1 but of still another embodiment; and

Fig. 6 is a circuit diagram applicable to the embodiments shown in Figs. 1-5.

Referring now to Figs. 1-2, a shallow tray 1,

shown in dotted lines in Fig. 2, is adapted tohave food to be cooked placed therein. This tray is made of material which is transparent to microwave energy and is supported by means of horizontal ears la, in and by an apertured shelf 2 which is mounted for horizontal sliding movement in a fixed support or frame 3, as by means of two pairs of inwardly-projecting upper and lower members 4 and 5 engaging each side of said shelf, said members being fixed to the opposite side walls of frame 3. Shelf 2 is shown in its closed position, and is adapted to travel to the left in Fig. 1 toward its open position, and thereafter to the right in Fig. 1 to be again closed.

A pair of horns or hollow waveguides B are fixedly mounted side by side in frame 3 as shown in Fig. 2, these horns having open upper ends and being so positioned that their open ends are located immediately below the bottom of tray 1- that radio-frequency energy is propagated down horns 6 only when there is food in tray I, thereby insuring that the magnetron will not be operating under conditions which would tend to produce undesirably high standing wave ratios, I proceed as follows:

A microswitch I is connected in a circuit, as described below, to control the circuit between the power supply of the magnetron or magnetrons and the magnetrons themselves. This circuit is arranged in such a way that when said switch is closed, the circuit between the magnetron power I supply and the magnetron is completed and the magnetron is put into operation to serve as a source of microwave energy, but when said switch is open the magnetron will be disconnected from the power supply and will not be in operation to produce radio-frequency energy. Microswitc'n 1 has an actuating button 8 and a pair of leads 9 and I connected thereto.

Microswitch l is fixed to the side wall of frame 3 and has an elongated resilient arm [I secured thereto in such a position as to cooperate with button 8 to depress said button to close said switch. The free end of arm H is fastened to a yoke structure i2 which supports, in a suitable bearing, a roller 13. In addition to the resistance to upward motion of roller l3 from a normal position provided by the resilience of arm ll, additional resistance to upward motion of said roller may be provided by a doubled-back flat spring member l4, one end of which is fixed to the side wall of frame 3, the free end of spring member l4 being adjustablyconnectedto roller l3 by means of a bolt i5 which is threadedly connected to said member and the lower end of which bears on the upper surface of yoke l2.

A lever arm it is pivotally connected by means of a pin 259 to the underside of shelf *2 and is vertically aligned with roller I3, as shown in Fig.

2. An upwardly-projecting pin H is fixed to the front end of arm it and is adapted to extend upwardly above shelf 2 through a suitable aperture l8 therein. Pin El and aperture it are so located in shelf 2 that the lower surface of one of the ears Ia of tray I will engage the upper end of pin ll when tray l is placed in the aperture in shelf 2. Rearwardly of pivot pin it, arm It is made substantially thicker, and the thickness of said arm increases from the end thereof toward the pivot point thereof to provide an integral cam surface Mia which is adapted to extend above shelf 2 through a suitable aperture is provided therein rearwardly of aperture l8. Roller I3 is adapted to engage and roll along the cam surface l 60. when said surface is moved with respect,

to said roller by the'sliding movement of shelf 2.

Due to the increased thickness of arm 56 at end Ifia, this end has more weight than the front end of said arm, so that arm i 6 normally assumes a position in which the upper surface of the front end thereof contacts the lower surface of shelf 2, in which cam surface Ilia projects only very slightly above the upper surface of shelf 2, and in which pin ll extends a substantial distance above the upper surface of said shelf. Therefore, when shelf 2 is slid toward closed position when no tray is on said shelf, cam surface ifia will be in its lowermost position and will remain in this position as shelf 2 is slid closed. In this lowermost position, cam surface liia will be too low to engage roller it (said roller being held in a normal position which is above the lowermost position of said cam surface by relatively stiff arm Ii), so that as shelf 2 is slid closed, switch 7 will remain in its normally open position and the magnetron will remain unconnected to its power supply, so that no radio-frequency energy is produced by said magnetron.

When an empty food tray i is placed in shelf 2, one of the side ears la thereof contacts the upper end of'pin H. The weight of the empty tray is sufficient to force pin I! down until its upper end is flush with the upper surface of shelf 2, pivotingarm it in acounterclockwise direction and raising cam surface lfia a substantial distance above the upper surface of said shelf, the position of arm It then being as indicated in dotted lines in Fig. 1. However, as shelf 2 is moved toward itsclosed position, roller 13 now comes in contact with cam surface Ilia and rides thereon, due to the fact that said cam surface is now elevated. As'explained above, there is .4 substantial force opposing the upward motion of roller [3. The weight of the empty tray being insufficient to overcome this force, as shelf 2 is pushed toward the right, the roller l3 forces cam surface Eta downwardly, pivoting arm l8 clockwise and raising pin I? and the corresponding end of the empty tray upwardly until, in the closed position of the shelf 2, the lever arm l6 has the position shown in solid lines in Fig. 1. In this case, due to the downward motion of cam surface ifia, roller l3 and arm II have not been moved upwardly a sufficient amount for arm H to contact button 3 and close microswitch i, so that, again, switch 1 remains in its normally open position and the magnetron remains unconnected to its power supply. In this case, with no food in the tray, conditions the radio-frequency system would be such as to tend to establish a high standing wave ratio therein; however, in this case, the magnetron remains unenergized and is therefore ineffective to supply microwaveenergy to the system.

Now, if a tray full. of food is placed in shelf 2, arm I6 is pivoted in a counterclockwise direction as before, and cam surface Ida is again raised. Now, however, as shelf 2 is moved toward its closed position, cam surface I ta forces roller l3 upwardly, because the weight of the loaded tray is sufficient to overcome the force opposing upward motion of said roller. Considered in another way, the force inherent in springs I4 and II is insufficient to pivot arm [6 clockwise and raise one end of the loaded tray. Therefore, in the closed position of shelf 2 with a loaded tray, the positions of arm 16 and of roller 53 will be those indicated by dotted lines in Fig. 1. When roller I3 is in this position, arm H hasbeen moved upwardly a sufficient distance for it to contact button 8, thereby closing microswitch i to connect the magnetron to its power supply. When the magnetron is thus energized, microwave energy is supplied to the horns 6 to heat or cook the food in the desired manner. In this case, with the proper amount of food in the tray, conditions in the system are such as to make the standing wave ratio low, and the magnetron does not require and being supported in said aperture by means.

of an outstanding horizontal bead or rib 2211 which rests on the upper surface of shelf 2 im-' mediately contiguous to aperture 2 An elongated rather narrow slot 23 is cut through shelf 2, this slot extending at right angles to one'of the longer sides of the rectangular aperture 21 and communicating with said aperture near one of the two rear corners of the rectangle 2i, said slot extending rearwardly from aperture 21 for an appreciable distance. Slot 23 is made wider near its point of intersection with aperture 2.1, as at 23a.

Pivotally mounted on the upper side of shelf 2 is a lever arm 24. As is shown in Fig. 3, the portion of arm 24 rearwardly of the pivot pin extends horizontally for a little distance, after which the arm curves downwardly and rearwardly to provide an upper cam surface 24a. Forwardly of the pivot pin, arm 24 extends horizontally for a little distance, after which it turns substantially 90 and extends vertically to substantially the same horizontal plane as shelf 2. Thence arm 24 is narrowed, and this narrower portion 24b of the arm extends forwardly horizontally, in slot 23, the arm terminating in the same vertical plane as the rear edge of aperture 2!, por" tion 24b of the arm being sufficiently narrower than said slot to be capable of free movement therein. Arm 24 has a broadened portion 240 adjacent it outer end which corresponds to the portion 23a of slot 23; the upper surface of said portion 240 is adapted to lie in the same horizontal plane as the adjacent upper surface of shelf 2 and the outer end of portion 240 is adapted to lie in the same vertical plane as the adjacent rear Wall of aperture 2!.

A microswitch i having an actuating button 8 is attached to frame 3. A resilient arm 25 is fastened to switch i in a position suitable for contacting button 8 to depress the same, thereby closing the normally-open switch. A roller 26, similar to the roller iii of Fig. l, is mounted in a suitable bearing, the fixed portion of which is attached to arm 25, in such a way that when said roller is moved upwardly from its normal position, arm 25 will be moved upwardly to contact button 8 and close microswitch '1. Microswitch 1 and its roller 26 are mounted in such a position that, as shelf 2 is pushed rearwardly to the closed position, aid roller will engage and ride on cam surface 24a to either actuate or be actuated by lever arm 24.

The weights of the portions of lever arm 24 on opposite sides of its pivot pin are so proportioned with respect to each other that said arm is normally balanced in a position in which portions 24b and 240 thereof lie substantially in a horizontal plane, as shown in solid lines in Fig. 3. In this normal position, roller is will engage cam surface 24a as shelf is closed. Now considering what happens when no tray .22 is in shelf 2 as it is closed, roller 26 first contacts the lowermost portion of cam surface 24d and rides thereon as shelf 2 is pushed farther closed or to the rear. As roller 26 rolls on the upwardly-convex portion of said cam surface, roller 25 tends to remain in the same horizontal plane due to the natural resistance to upward motion of resilient arm 25, and there is no weight acting on the outer end of lever arm 24 to oppose the pivotal movement of said arm. As a result, the force acting on roller 26 pivots lever arm 24 in a clockwise direction, said arm reaching the position shown in dotted lines in Fig. 3 when shelf 2 is in its closed position. In this case, roller 2-3 remains in its normal lowermost (or dotted-line) position when shelf 2 is closed, and switch 5 remains unactuated or open. Therefore, the magnetron which is connected to the radio-frequency horns remains unenergized and no radio-frequency energy is propagated up said horns.

Now we will consider what happens when an empty tray 22 is in shelf 2 as it is closed. Now there is some weight applied through rib 22a onto the upper surface of portion 240 of the lever arm, this weight tending to oppose, somewhat, upward motion of portions 241) and 246, or in other words tendingto oppose somewhat clockwise pivoting of the lever arm 24. However, the weight of the empty tray 22 is still insuflicient to overcome the downward force exerted on roller 26 by the resilience of arm 25. Therefore, as shelf 2 moves to the rear to its closed position, lever arm 24 again pivots in a clockwise direction, said arm reaching the position shown in dotted lines in Fig. 3 when shelf 2 is in its closed position. In this case, as portion 240 of the lever arm moves upwardly it, by its engagement with rib 22a, lifts the rear portion of tray 22 bodily upward. Roller 26 again remains in its normal or original dottedline position because of the pivoting of lever arm 24, so that microswitch I again remains open and the magnetron unenergized; no radio frequency energy is propagated along horns 6.

Next we will consider what takes place when a tray 22 containing a predetermined weight of food 2! is supported in and by shelf 2 as said shelf is closed. A substantial weight is now applied through rib 22a onto the upper surface of portion 240 of the lever arm, this weight opposing upward motion of portions 241) and 240 of said arm; The weight of the full or loaded tray 22 is sufficient to overcome the downward force exerted on roller 26 by arm 25. Therefore, as shelf 2 moves to the rear toward its closed position, arm 24 does not pivot, but remains substantially in the position indicated in solid lines in Fig. 3. Roller 26 is forced vertically upward by the upwardlyconvex cam surface 24a as shelf 2 is pushed to the rear, said roller reaching its uppermost (or solid-line) position when shelf 2 is closed. Switch 7 is closed in response to the upward movement of roller 26 and arm .25, thereby energizing the magnetron to supply radio-frequency energy to horns 6. This energy propagates upwardly in horns 6, flowing out the upper open ends thereof to impinge on food 21 to heat or cook the same.

It will be apparent that in this embodiment, also, a weight-responsive switch has been provided for a cooker, in which the magnetron is energized only when there is'food in the food tray.

Now referring to Fig. 5, another embodiment of the weight-responsive microswitch operating means is shown. Again, a shelf 2 is mounted for horizontal sliding movement with respect to a fixed frame 3. Shelf 2 has a rectangular aper ture 28 therein, and at the edges of said aperture flanges 29 extend downwardly on all four sides of said aperture, these flanges preferably extend ing down below the upper ends of horns 5. The rear flange 29 has a slot 29 cut therein, this slot extending upwardly from the bottom edge of said flange and being of sufficient width and depth to allow said flange to pass over the ends of horns 6 when shelf 2 is moved from front to rear, or from open to closed positions (that is, from left to right in Fig. 5).

A pair of horizontally extending spaced support rods 30 have their opposite ends fixed in the front and rear flanges 25-, these rods being made of a suitable material, for example a plastic, which is transparent to radio-frequency energy. A food tray 3! is adapted to be supported on and by rods 30 within aperture 28, this tray being prevented from moving sidewise by having a pair of upwardly-extending ribs on the bottom surface thereof which fit closely over the rods 30. Tray 3| is rectangular in cross-section, and said tray has a greater cross-sectional area at its top than at its bottom, so that the side walls thereof taper inwardly from top to bottom.

A microswitch 1, having an actuating button 8 and a resilient actuating arm 32, is fixed to frame 3. -A horizontally-extending actuating rod 3'3, made of-insulating material, has one end attached to arm 32,:its oppositeend being-adapted to extend through -a suitable aperture provided in rear flange 29 and'lto contact the rear side wall of tray 31 when shelf 2 is pushed rearwardly to its closed position. The outerend of rod 33 has an upwardly-beveled face, as shown, and said rod is positionedso-as to contactthe rear side wall of tray 3| :near the lower end of said side wall. It will be seen that when rod 33 is pushed to the right by tray .31, 'microswitch 7 will be actuated toits closed position, but when said rod is not pushed to the right, said switch will not be actuated.

When shelf '2 is slid 'rearwardly to its closed p.osition,but is'trayless, there will be nothing to touch-rod 33 when shelf "2 is closed, so that switch Twill remainin itsncrmally-ppen dotted-*line'position'and the magnetron will remain unenergized, so that "no radio-frequency energy will be produced to be propagated along horn or Waveguide "6.

i-Now'assuming'thatan empty tray 31 has been placedonshelfd and it is being slid rearwardly or to the right to its closed position, the beveled edge of rod 3-3 willcome .into contact with the rear side wallof tray -31. Since the empty tray is very light, and since "arm 32 has some resistance to movementthereof, due to its resilience, the beveled edge of rod33 will slide-along the inclined surface of the rear side wall of the tray, lifting the tray vertically, as shown by dotted lines. Because the tray is lifted, rod 33 is not moved horizontally, but remains in its left or dotted-line position, in which theswitch 1 is unactuated, and the magnetron is unenergized. Therefore, no radio-frequency energy is produced by the magnetron.

Now assumingthat a tray 3! loaded with food 34- hasbeenplacedon shelf Zand the shelf is being closed, the-beveled'edge of rod 33 again will come into contact with the rear side wall of the tray 3|. In this case the tray has substantial Weight, so that it presents relativelygreater resistance to upward motion by rod 33. This resistanceof the trayis sufilcient to overcome the inherent resistance to movement of arm '32, so that the tray isnot liftedbut remains in the'position shown in solid lines and, as shelf 2 is slid home, the rod'33 does not slide along the tray wall, but is pushed thereby to the right to the position shown in solidlines.

This means that 'microswitch "'l is actuated to its closed position, in which the magnetron is energized. Therefore, radio-frequency energy is propagated along the horn'fi, flowing out the upperopen end thereof to impinge "on food 34 and heat or cook the same.

Here, as in the other embodiments, a weightre'sponsive switch has been provided for a cooker, in which the magnetron is energized only when there'is food-in the food tray.

Fi'g.-6 shows a-circuit in whichthe weight-actuated *or -weight-responsive microswitch "i of any orall of the embodiments maybe utilized for control purposes. Lead it, of microswitch "l is connected directly-to one side of an alternating current source, while lead 9 of said'microswitch is connected, in series with the operating winding 3.5'-of=asensitive relay 35, to the oppositaside of said so'u'rce, so that when microswitch liscl'osed, relay 35 will be energized. Theflnormallyopen contacts 31 of relay 36 are "connected, in series with the operating winding 38 Of a power relay 39, 'a'c'ross the source, so that when contacts :31

are closed by the energization of :relay fim relay 39 will :be energized.

'I he normally-open contacts ill of relay '39 are connected, in'series with the primary winding '41 of atransformer 42, acrossthe A. C. source. The ends 'o'f'the centertapped secondary winding 13 of transformer 42, as well asthe centertap thereof, are connected asthe input for a controllable 'fullwave rectifier and :filter circuit 2 1, which'may'be of any'desired'type having a positive output terminaldfi'and a'negative output terminal MS. The terminal 35 vis'connected to the anode M of ;a magnetron lhwhile the terminal 36 is'connected tothecathode .49 of said magnetron. A suitable coupling "device 5% couples the radio-frequency energy output of magnetron E8 to the horns such asJS.

Whenmicroswitch l is actuated to its closed position, the voltage of the source is applied-to primary winding 'dl, this being accomplished through the action of relays 36 and 39. This voltageapplied to winding ll provides an 'input for circuit M, which in turnprovides arectified high-voltage output for the energization of magnetron and the consequent production of radic frequcncy energy therefrom. In this case, the radio-frequency energy source -48 is turned on. When microswitch l is open, it can be seen that windingfil is open-circuited, so that there is no input for circuit i l and consequently no higlnvoltage output therefrom :for energization of the-magnetron. Inthis case, the radio-frequency energy source 48 is turned ofi.

It will be seen,-.from' all of the above, that I'have provided a weight-responsive microswitch for microwave cookers, which-functions to turn on or connect the radio-frequency energy source-toe. power supply when there is a predetermined weight of food in the food tray, and which functions to leave said source-turned off or disconnected from its power supply when the food tray has less than-a predetermined weight.

Ofcourse, it is to be understood that this invention is not limited'to the particular details as described above, as many equivalents will suggest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope'of this invention within the art.

what iscclaimed is:

1. A control device for cookers comprising a container for holding food, a source of heat, means for supporting saidcontainer, said means being movable withrespectto said source ofheat, a switch for controlling said source, and means actuated by movement of said container by said supporting'mean's into I heat transferring relation with-said source, and responsive to the weight of s'aid 'container and said food for controlling "said switch.

2. A control device for cookers comprising a container for holding food, a source of heat, means for supporting said container, said means being movable with respect to said source of heat, a switch for controlling said source, and means actuated by movement'of said container by said supporting'means into heat transferring relation with said source, and responsive to the weight of said container and said food for controlling saidswitch, saidmeans acting to 'close said switch when said container and food have more thana pr edetermined weight.

3. A control device for cookers comprising :a container for'holding food, a'source of heat comprising :microwave energy, means for supporting said container, said means being movable with respect to said source of heat, a switch for controlling said source, and means actuated by movement of said container by said supporting means into heat transferring relation with said source, and responsive to the weight of said container and said food for controlling said switch, said means being effective to leave said switch open when said container and food have less than a predetermined weight.

4. A control device for cookers comprising a container for holding food, a source of heat, means for supporting said container, said means being movable with respect to said source of heat, a switch for controlling said source, and means actuated by movement of said container by said supporting means into heat transferring relation with said source, and responsive to the weight of said container and said food for controlling said switch, said means acting to close said switch when said container and food have more than a predetermined weight and being effective to leave said switch open when said container and food have less than a predetermined weight.

5. A control device for cookers comprising a container for holding food, a source of heat, means for supporting said container, said means being slidable with respect to said source of heat, a switch for controlling said source, and means actuated by movement of said container by said supporting means into heat transferring relation with said source, and responsive to the weight of 10 said container and said food for controlling said switch.

6. A control device for cookers comprising a container for holding food, a source of heat, means for supporting said container, said means being slidable with respect to said source of heat, a switch for controlling said source, and means actuated by movement of said container by said supporting means into heat transferring relation with said source, and responsive to the weight of said container and said food for controlling said switch, said means acting to close said switch when said container and food have more than a predetermined weight and being effective to leave said switch open when said container and food have less than a predetermined weight.

MARVIN J. BOCK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 799,377 Harden Sept. 12, 1905 1,699,610 Del Riccio Jan. 22, 1929 1,994,629 Arkema Mar. 19, 1935 2,013,172 Petrone Sept. 3, 1935 2,378,816 Wild June 19, 1945 FOREIGN PATENTS Number Country Date 122,019 Switzerland Aug. 16, 1927 

